全文获取类型
收费全文 | 64491篇 |
免费 | 283篇 |
国内免费 | 589篇 |
专业分类
系统科学 | 1261篇 |
丛书文集 | 568篇 |
教育与普及 | 286篇 |
理论与方法论 | 541篇 |
现状及发展 | 35029篇 |
研究方法 | 1306篇 |
综合类 | 24181篇 |
自然研究 | 2191篇 |
出版年
2013年 | 826篇 |
2012年 | 745篇 |
2011年 | 2843篇 |
2009年 | 621篇 |
2008年 | 979篇 |
2007年 | 1122篇 |
2006年 | 1178篇 |
2005年 | 1317篇 |
2004年 | 2441篇 |
2003年 | 2055篇 |
2002年 | 1763篇 |
2001年 | 1757篇 |
2000年 | 1249篇 |
1999年 | 1194篇 |
1998年 | 651篇 |
1997年 | 776篇 |
1996年 | 540篇 |
1994年 | 684篇 |
1993年 | 691篇 |
1992年 | 1121篇 |
1991年 | 902篇 |
1990年 | 1022篇 |
1989年 | 860篇 |
1988年 | 803篇 |
1987年 | 879篇 |
1986年 | 879篇 |
1985年 | 1064篇 |
1984年 | 908篇 |
1983年 | 736篇 |
1982年 | 859篇 |
1981年 | 897篇 |
1980年 | 1020篇 |
1979年 | 1654篇 |
1978年 | 1482篇 |
1977年 | 1486篇 |
1976年 | 1267篇 |
1975年 | 1278篇 |
1974年 | 1291篇 |
1973年 | 1451篇 |
1972年 | 1539篇 |
1971年 | 1566篇 |
1970年 | 1765篇 |
1969年 | 1513篇 |
1968年 | 1479篇 |
1967年 | 1349篇 |
1966年 | 1131篇 |
1965年 | 872篇 |
1964年 | 516篇 |
1958年 | 709篇 |
1957年 | 563篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
511.
Summary Roots ofVicia faba L. immersed in a buffer solution were found to release esterases into the environment. The substrate -naphthylacetate was taken up by the roots and degraded, the hydrolysis products being released back into the surrounding medium. 相似文献
512.
F. Baccichetti F. Bordin F. Carlassare 《Cellular and molecular life sciences : CMLS》1979,35(2):183-184
Summary Furocoumarin photosensitization induces -prophage from lysogenicEscherichia coli cells; this effect is clearly due to the photoreaction that furocoumarins give with DNA, and it appears connected with the formation of monoadducts rather than of diadducts (cross-links).Acknowledgments. The authors wish to express their thanks to Dr L. Conventi, Microbiology Institute of Padua University, for generously donating theE. coli strains used in this work. 相似文献
513.
Summary In a group of 5 women taking oral contraceptives, the concentration of polymorphonuclear leucocytes along the gingival margin and the activities of cathepsin D, -glucuronidase and elastase were found to increase significantly during the intermenstrual phases.Supported by grant 3.604.075 of the Swiss National Fund for scientific Research. The authors thank Dr M. Baggiolini and Prof. A. Linder for the helpful advices. 相似文献
514.
C Radanyi G Redeuilh E Eigenmann M C Lebeau N Massol C Secco E E Baulieu H Richard-Foy 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(2):255-258
The antibodies against estrogen receptor were obtained after injecting Rabbits with a cytoplasmic receptor fraction isolated from Calf uterus. The estrogen receptor was partially proteolysed by the action of trypsin and subsequently purified by affinity chromatography (purification 4,000 to 10,000 fold, to a purity of 5-20%). The affinity of the antibody for the proteolysed receptor is KD approximately 1 nM and serum titres have reached values of approximately 50 nM. The values remained constant after the third injection. Preliminary results indicate that the antibody has approximately the same affinity for "native" cytoplasmic estrogen receptor from Calf uterus, as well as for the "trypsinized" forms of estrogen receptor isolated from Calf uterine cytosol and Hen oviduct nuclei. 相似文献
515.
A Jost M Rieutort J Bourbon 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(3):347-349
Day 25 after insemination is a date of peculiar importance in the maturation of several organs in the Rabbit fetus. From day 25 onward the fetal liver stores increasing amounts of glycogen and the lung stores increasing amounts of lecithins, concomitant with sudden rise in the activity of lung phosphatidic-acid phosphohydrolase. Earlier studies on decapitated fetuses established that glycogen storage in the liver is dependent on a dual hormonal control, comprising a pituitary hormone like growth hormone or prolactin (some placental hormones share the same activity) and corticosteroids (Jost, 1961). Since the variations in endogenous corticosteroids do not seem to herald these liver or lung changes (Mulay et al., 1973), a study was made of growth hormone. Plasma immunoreactive growth hormone--determined with a heterologous Rat system (Kervran et al., 1976)--increases eightfold between days 23 and 25. During the same time plasma prolactin does not change according to McNeily and Friesen, 1978, and to unpublished data obtained with Dr McNeilly. In preliminary assays, Rat growth hormone was seen to increase phosphorylase "a" activity in the lung of 18.5 day-old Rat fetuses, thus anticipating normal development. We suggest that growth hormone plays a role in initiating liver and lung maturation. 相似文献
516.
M Goustard 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,288(21):1615-1618
The "great call" of adult male and female Hylobates concolor leucogenys was studied in different conditions of social stimulation, using quantitative (i. e. sonographic) analysis. Vocal sequences are generally made up of mixed sounds, appearing in a fixed order and constituting a species-specific character. Qualitative diversification appears in the repetition of sequences. Different social situations alter parameters of the calling pattern: especially the length and intensity of homologous modulated sounds, and the qualitative complexity of sequences. The capacity of controlling length and intensity of modulated sounds has been shown in earlier papers for H. c. gabriellae, and by several authors, in Cebus and Rhesus monkeys. The "great call" of H. c. leucogenys shows the two fundamental characteristics of instinctive (i. e. genetically determined) activity-patterns. 相似文献
517.
Summary Synthetic 3-methylcyclohex-3-en-1-one, or 3,3-MCH, decreased by 77% the flight aggregation ofDendroctonus pseudotsugae (Scolytidae) to sticky traps containing attractant (frontalin, -pinene, and resin). However, windthrown trees were protected by 3,3-MCH much less than is known to occur with the isomer 3,2-MCH.This research was supported in part by NSF grants BMS 72-02522 and DEB 77-11361 and the O.S.U. School of Forestry. We thank the administration of the Siuslaw National Forest for study sites, and Dr L.M. Libbey for GC/MS of 3,3-MCH. Oregon State University Ag. Exp. Sta. Tech. Paper No. 4313. 相似文献
518.
Summary Microelectrophoretic administration of D--aminoadipate reversibly reduced excitatory responses of cat dorsal horn neurones evoked by iontophoretic glutamate and non-noxious peripheral stimuli but did not influence similar responses evoked by noxious peripheral stimuli or iontophoretic substance P. 相似文献
519.
Summary The active calcium transport along the small intestine of adult rat was shown to exhibit daily rhythmic variations of considerable amplitude. Both the light-dark cycle and the time of food presentation acted as synchronizers of the rhythm observed.This work has been supported by Polish Academy of Sciences within the project MR II.1.1.6. 相似文献
520.
Summary InTambourissa religiosa (Monimiaceae), the flowers are pollinated at a hyperstigma formed by the mouth of the floral cup, and not at the carpels. This is an extraordinary feature in angiosperms.I thank Professor Dr W. Rauh, Institut für Systematische Botanik und Pflanzengeographie der Universität Heidelberg, for providing material from his green house collection (W. Rauh, No. M 138, coll. 1959) and Dr Christa Güssefeld-Schneider for fixing pollinated flowers. 相似文献